Petroleum wax for paper coatings



United States Patent Ofltice 3,053,677 PETRQLEUM WAX F012 PAPER COATINGSGeorge P. Touey, Kingsport, Tenn, assignor to Eastman Kodak Company,Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Nov. 12,1959, Ser. No. 852,225 7 Claims. (Cl. 1ll6162) This invention concernsan improved type of petroleum wax for use in wax coating compositions,more particularly petroleum wax modified with an aliphatic acid ester ofa sugar.

Petroleum waxes are well known in the paper coating field used formaking waxed paper of various types. Waxed papers of this type are cheapand highly eflicient in producing water-proof paper containers such asmilk cartons, paper cups and the like for various types of beverages.These Waxed papers are also used for wrapping various food items toprotect them from dirt, dehydration, moisture and the like.

Not only are wax coatings inexpensive but they have the desirablefeatures of being free flowing liquids in the melted state, frequentlymelting under 100 C. permitting paper to be coated by simply dipping orpassing the paper through a hot melt of the material.

Although petroleum wax coatings are used extensively to water-proofpaper, they have several shortcomings which have not been previouslyresolved successfully. For instance, they have poor scuff-resistance andpoor resistance to impact. This means that the coatings are oftenscraped off of the paper in normal usage or are easily shattered by aheavy blow. Another disadvantage is that the coatings, being extremelynon-polar in character, often do not bond sufiiciently to the paper topermit folding of the paper without having the wax coating flake off.

As a means of avoiding these disadvantages, it has been suggested thatplasticizers be added to the wax formulations to reduce their tendencyto flake and to make them adhere more firmly to paper. However, thecommon plasticizers are not compatible with petroleum wax. Usually thepl-asticizer is not sufliciently soluble in the wax or in the event thatit is soluble, it gradually exudes to the surface of the coatingproducing a sticky or glossy film.

We have discovered a more compatible plasticizer for petroleum wax whichnot only is compatible with petroleum wax but also provides a betteradherence to the paper surface and reduces flaking when the paper isbent or folded.

One object of this invention is to disclose a new type of additive forpetroleum waxes designed for coating operations. Another object is todisclose a new type of additive which is highly soluble in the wax andwhich will not exude to form a glossy or tacky surface. A third objectis to disclose a new type of Wax formulation which will bond more firmlyto the paper than the petroleum wax alone. A fourth object is todisclose a new and more compatible plasticizer for petroleum wax. Theseobjects are accomplished by blending certain types of sugar esters withthe Wax before it is used as a paper coating. The esters aresubstantially completely esterified aliphatic acid esters of glycose,sucrose, sorbitol and the lower alkyl glycosides such as methylalpha-D-glycoside and ethyl alpha-D-glucoside.

The amount of sugar ester required depends on the type of ester and theamount of plasticizing and enhanced bonding action of the wax desired.Thus for som-epaper surfaces only as little as 2% of the sugar acidadditive is all that is required, whereas in other applications theconcentration of the sugar additive may be as high as 25%. Normally,however, a concentration of 3-15 parts sugar ester to 97-85 parts ofpetroleum wax is sufficient. Higher concentration of sugar esters,althoughsuitable for certain specialized operations usually tend to makea tacky wax coating. The preferred concentra tion for general use inpaper coatings is 3-10 parts sugar ester and 97-90 parts petroleum wax.

The sugar esters which function as plasticizers and bonding agents forthe petroleum waxes are the substantially completely esterifiedaliphatic acid esters (containing 3-8 carbon atoms in their acylsubstituents) of glucose, sucrose, sorbitol, methyl a-D-glucoside. Thus,the propionic, butyric, isobutyric, valeric, isovaleric, hexanoic,isohexanoic, heptanoic, octanoic, and 2-ethylhexanoic acid esters ofthese sugars may be employed. Also the aliphatic acids can beunsubstituted as in the case of crotonic, methacrylic, and the like.

Sugar esters with aliphatic acyl groups containing more than '8 carbonatoms such as, for example, sucrose octapalmitate or octaoleate areundesirable. These are not sufiiciently compatible with the wax andgradually exude to the surface of the wax after standing several weeks.The aromatic acid esters are undesirable for similar reasons. Inaddition, aromatic acid esters of sugars in general are considered moretoxic than the aliphatic acid esters.

The preferred sugar esters are the isobutyrate esters of glycose,sucrose, sorbitol and methyl (or ethyl) alpha- D-glucoside. They can bemade by inexpensive procedures, impart no objectionable odor to the Wax,and they have a sufiicient number (4) of carbon atoms on their acylsubstituents to provide the proper amount of solubility in the wax.Also, they are completely waterinsoluble and are quite stable to heat.The glucose and per 1 sugar molecule since the presence of asubstantial.

amount of unesterified hydroxyl groups in the product tends to make itless compatible with the wax.

The petroleum waxes of this invention are those hydrocar'bon fractionswhich have a melting point range of from above about 40 C. to about 96C. The main two waxes in this classification are the paraffin waxes(melting point 4366 C.) and the microcrystalline' waxes (melting point63-94 C.). These are the pe troleum waxes used by the paper coatingindustry. is understood, however, that these waxes can contain a minorproportion of the various polyolefin waxes. polyolefin waxes may be usedin concentrations up to 1 part polyolefin wax to 9 parts petroleum waxwithout any eifect on the compatibility of the sugar esters with thepetroleum wax.

EXAMPLE 1 This example illustrates the compatibility of the sugar estersof this invention with a standard grade of paraffin wax (M.P. 55 C.). 1

Ten grams of the sugar ester (Table I) was mixed with g. of the meltedparaflin wax at a temperatureof C. When thoroughly mixed, the hotsolution was rated for its clarity. A clear solution indicated thatthesugar derivative had dissolved completely in the wax,

whereas a hazy solution or a two-layer system den0ted'- incompatibility.

Patented Sept. 11, 1962 However, this amount:

The

After the compatibility test was performed, the melted wax was thenpoured into a shallow dish, whereupon it solidified. The solidifiedproduct was stored for one week at 78 F. and 55% relative humidity. Anyexudation of the sugar ester was noted after this storage period.

Table I Compatibility Observation of Sugar Ester Rating at 100 C.Exudation Glucose pentaacetate Insoluble Crystals of sugar ester onsurface.

Glucose pentapropionate Partly soluble..- A trace of sugar estercrystals on the surface.

Glucose pentabutyrate No exudation.

Glucose pentaisobutyrate..- Do.

Glucose pentavalerate. Do.

Glucose pentadecanoate- Slightly greasy surface.

Glucose pentaolcate Ggeasy liquid on sura Insoluble Partly solublece.Sucrose octaacetate Crystals of sugar ester on surface. A trace of sugarester crystals on surface.

No exudation.

Sucrose octapropionate Sucrose octabutyratc Sucrose octaisobutyrate Do.Sucrose octavalerateu Do. Sucrose octa-Z-ethyl-h Do.

anoate. Sucrose octadecauoate Slightly greasy surface, Sucroseoctastearate- Greasy solid particles.

Sorbitol hexaacetate Crystals of sugar ester on surface.

Sorbitolhexapropionatenne A trace of sugar ester crystals on thesurface.

Sorbitol hexabutyrate No exudation.

Sorbitol hexaisobutyrate D0.

Sorbitol hexavalerate Do.

Sorbitol hexa-Q-ethyl-hexa- Do.

noate. Sorbitol hexaoctadecanoate. Slightly greasy surface.

Sorbitol hexapalmitate Methyl a-D-glucoside tetraacetate.

Methyl a-D-glucoside tetraproplonate. Methyl a-Dglucoside tetra- Greasysolid particles on surface.

Crystals of sugar ester on surface.

No exudation.

Do. butyrate. Methyl a-D-glucoside tetra- Do.

isobutyrate. Methyl a-D-glucoside tetra- Do.

valerate. Methyl a-D-glucoside tetra Slightly greasy surface.

2-ethyl-hexanoate. Methyl a-D-glucoside tetra- Do.

octadecauoatc.

Greasy surface.

The compatibility tests show that the sugar esters with acylconstituents containing more than 8 carbon atoms are compatible with themelted wax but gradually exude to the surface of the wax when itsolidifies. This is probably because they are not sufficiently solublein the wax at room temperature. The sugar acetates and some of thepropionates were either insoluble in the melted wax or insoluble in itwhen it returned to room temperature. The tests also show that thoseesters with acyl carbon numbers between 3 and 8 were considerably moresoluble in the wax and had little or no tendency to exude to the surfaceof the solidified wax.

EXAMPLE 2 This example illustrates how the wax coatings containing thewax-compatible sugar esters did not flake off when the coatings werebent.

An uncoated milk-carton grade of heavy paper was cut into strips of 2" x6". A strip of this paper was submerged in each of the hot melts shownon Table II for minutes. The temperature of the melts was maintainedbetween 95 and 100 C. during this operation. After the strips werethoroughly wetted with the liquid wax, they were removed and allowed tocome to room temperature. They were then stored for 24 hours at 78 F.and 55% relative humidity before they were tested.

The coated strips were bent to an angle of 180 and the degree of flakingof the wax along the crease was observed. This operation was repeateduntil flaking of the wax in all cases was finally observed.

N umber oi Folds Required to Cause the Wax to Flake oil the Paper at theCrease Sugar Ester in the Wax Coating 1 1 Except for the controlcoating, all of the waxes consisted of parts paratfin wax and 10 partssugar ester.

This nonfiaking characteristic of the wax is caused by a two-foldeffect. The first is the more polar nature of the ester in comparisonwith the wax. This tends to give a stronger bond to the paper. The otheris the plasticizing action which the ester has on the wax.

The polyolefin waxes which can be admixed with the petroleum-sugar estercombinations of this invention are chosen from those polyethylene andpolypropylene waxes which are compatible with the petroleum waxes. Theirmolecular weights range from about 1000 to 10,000 and their meltingpoints are within the limits of 70 C. and C.

I claim:

1. A wax coating composition consisting essentially of a petroleum waxconsisting of those hydrocarbon fractions having a melting point rangeof from about 40 C. to about 96 C. and 040% of a polyolefin wax selectedfrom the class consisting of polyethylene and polypropylene waxes havinga molecular weight range of 1,000 to 10,000 and melting points withinthe range of 70 C. and 120 C., and 225%, based on the total weight ofthe composition, of a sugar ester, having an average of no more than onehydroxyl group per sugar molecule, selected from the class consisting ofthe esters of glucose, sucrose, sorbitol, and the lower alkyl glucosidesobtained by reacting the sugar with an acid selected from the classconsisting of propionic, butyric, isobutyric, valeric, isovaleric,hexanoic, isohexanoic, heptanoic, octanoic, 2-ethyl hexanoic, crotonic,and methacrylic acids.

2. A coating composition consisting essentially of a petroleum waxconsisting of those hydrocarbon fractions having a melting point of40-96 C. and 225%, based on the weight of the coating composition of asubstantially completely esterified isobutyrate sugar ester obtainedfrom glucose.

3. A coating composition consisting essentially of a petroleum waxconsisting of those hydrocarbon fractions having a melting point of40-96 C. and 225%, based on the weight of the coating composition, of asubstantially completely esterified isobutyrate sugar ester obtainedfrom sucrose.

4. A coating composition consisting essentially of a petroleum waxconsisting of those hydrocarbon fractions having a melting point of40-96" C. and 2-25%, based on the weight of the coating composition, ofa substantially completely esterified isobutyrate sugar ester obtainedfrom sorbitol.

5. A coating composition consisting essentially of a petroleum waxconsisting of those hydrocarbon fractions 5 having a melting point of40-96 C. and 2-25 based on the weight of the coating composition, of asubstantially completely esterified isobutyrate sugar ester obtainedfrom methyl-u-D'glucoside.

6. A coating composition consisting essentially of a petroleum Waxconsisting of those hydrocarbon fractions having a melting point of40-96 C. and 2-25%, based on the weight of the coating composition, of asubstantially completely esterified isobutyrate sugar ester obtainedfrom ethyl-a-D-glucoside.

7. A Waxed paper comprising a paper substrate having thereon a coatingcomposition consisting essentially of a petroleum wax consisting ofthose hydrocarbon fractions having a melting point range of from about40 C. to about 96 C. and 010% of a polyolefin Wax selected from theclass consisting of polyethylene and polypropylene Waxes having amolecular weight range or" 1,000 to 10,000 and melting points within therange of 70 C. and 120 C., and 225%, based on the total weight of thecomposition, of a sugar ester, having an average of no more than onehydroxyl group per sugar molecule, selected from the class consisting ofthe esters of glucose, sucrose, sorbitol, and the lower alkyl glucosidesobtained by reacting the sugar with an acid selected from the classconsisting of propionic, butyric, isobutyric, valeric, iso- Valeric,hexanoic, isohexanoic, heptanoic, octanoic, 2-ethyl hexanoic, crotonic,and methacrylic acids.

References Cited in the file of this patent UNITED STATES PATENTS2,094,771 Charch Oct. 5, 1937 2,108,808 Finzel Feb. 22, 1938 2,322,198Parsons June 15, 1943 2,700,022 Clayton Ian. 18, 1955 2,733,225 SmithIan. 31, 1956 2,783,156 Oathont Feb. 26, 1957 2,791,510 Sproule May 7,1957 2,893,990 Haas July 7, 1959 2,908,681 Anderson Oct. 13, 1959

1. A WAX COATING COMPOSITION CONSISTING ESSENTIALLY OF A PETRELEUM WAXCONSISTING OF THOESE HYDROCARBON FRACTIONS HAVING A MELTING POINT OFFROM ABOUT 40*C. TO ABOUT 96*C. AND 0-10% OF A POLYOLIFIN WAX SELECTEDFROM THE CLASS CONSISTING OF POLYETHYLENE AND POLYPROPYLENE WAXES HAVINGA MOLECULAR WEIGHT RANGE OF 1,000 TO 10,000 AND MELTING POINTS WITHINTHE RANGE OF 70*C. AND 120*C., AND 2-25%, BASED ON THE TOATAL WEIGH OFTHE COMPOSITION, OF A SUGAR ESTER, HAVING AN AVERAGE OF NO MORE THAN ONEHYDROXYL GROUP PER SUGAR MOLECULE, SELECTED FROM THE CLASS CONSISTING OFTHE ESTERS OF GLUCOSE, SUCROSE, SORBITOL, AND THE LOWER ALKYL GLUCOSIDESOBTAINED BY REACTING THE SUGAR WITH AN ACID SELECTED FROM THE CLASSCONSISTING OF PROPIONIC, BUTYRIC, SIOBUTYRIC, VALERIC, ISOVALERIC,HEXANOIC, ISOHEXANOIC, HEPTANOIC, OCTANOIC, 2-ETHYL HEXANOIC, CROTONIC,AND METHACRYLIC ACIDS.